SYNTHESIS AND STRUCTURAL CHARACTERIZATION OF K(MOO2)(PO4).H2O, AND ITS TOPOTATIC REACTION TO FORM KMOO2PO4

K(MoO2)(PO4) · H2O crystallized in the monoclinic space group P21 n with lattice parameters a = 5.846(1) Å, b = 8.626(1) Å, c = 12.364(1) Å, β = 102.80(1)°, and z = 4. It was synthesized under hydrothermal conditions from a mixture of MoO3, MoO2, and K2HPO4. The structure was refined to R = 0.037 with 1223 reflections for which I > 3σ. Its structure consists of alternating molybdenum-oxygen octahedra and phosphate tetrahedra forming four- and eight-membered rings. The rings are connected through alternating polyhedra to form sheets. Potassium ions are located between the layers above and below the eight-membered ring. Upon heating to 500°C water splits out and the layers collapse to form the three-dimensional molybdenum phosphate KMoO2PO4. This compound crystallizes in the orthorhombic space group Fddd with the cell parameters: a = 12.209(4) Å, b = 15.535(2) Å, c = 11.149(4) Å. The structure was determined and refined to R = 0.046 using 464 reflections with I > 3σ. The coalescence of layers results in a three-dimensional framework structure containing tunnels in which the K+ ions reside. © 1991.